The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Known internal combustion engines operate at predetermined air/fuel ratios. The air/fuel ratio can be controlled by determining mass air flow into the engine and controlling engine fueling based thereon. The mass air flow can be measured using an air flow metering device or estimated based upon engine operating conditions using speed/density equations.
A known air flow metering device operates on the principle of anemometry, employing a sensing unit that can be a hot-wire device or a hot-film device. The sensing unit comprises a heated element placed within the air flow stream which can be maintained at a constant temperature differential above the ambient air temperature by the addition of electrical power. The amount of electrical power required to maintain the heated element at the proper temperature differential is directly related to the mass air flow rate past the sensing unit. It is known to communicate the amount of electric power to maintain the heated element of the sensing unit at the proper temperature to a control module as a digital signal consisting of a pulsewidth-modulated signal.
It is known that mass air flow into an engine can pulsate due to dynamic conditions in an engine intake system caused by engine throttling, opening and closing of intake valves and related air flow into engine cylinders, and other factors. It is known that such pulsation is most discernible in three, four, and five cylinder engines. The pulsation in the mass air flow can include reverse flow, i.e., air flow away from the engine. Pulsation and other conditions can introduce errors in measurement of mass air flow into the engine.